Why don't you think the browsers can agree on replacements? Most of the major browsers have proposals for replacing some piece of advertising-related third party cookies [1][2][3].
(Disclosure: I work on ads at Google, speaking only for myself)
I see this as a natural evolution of the web. The existing web standards and protocols no longer meet security or privacy user needs. Ideally, we do create better open standards. Apple’s Private Relay is great, but its gated off to paying customers.
If Google wasn't having anti-trust worries, maybe they could force it to happen, but it's too blatant now.
My assumption is 3rd party cookies die to regulation, and nothing gets enough consensus to replace them.